Metal-clad laminate and method for production thereof

ABSTRACT

A metal-clad laminate excellent in isotropy, appearance, bondability between a TLC polymer film and a metallic sheet, and dimensional stability is provided less costly with a first step of thermally compressing the film with the metallic sheet by passing them through a nipping region between heating rolls, and a second step of heat-treating the resultant metal-clad laminate at a temperature not higher than the melting point of the film, wherein the film has thermal expansion coefficient α L  satisfying α L =βT+γ with thickness T, thickness coefficient β and anisotropy coefficient γ of the film; wherein the coefficient β is within the range of −0.08 to −0.01; the coefficient γ is within the range of α M +6≦γ≦α M +10 with thermal expansion coefficient α M  of the metallic sheet; and thermal expansion coefficient α T  of the film is within α M −2≦α T ≦α M +3 with the coefficient α M .

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of prior U.S. patentapplication Ser. No. 11/718,843, filed May 8, 2007, the disclosure ofwhich is incorporated herein by reference in its entirety. The parentapplication was the National Stage of PCT/JP05/19781, filed Oct. 27,2005, the disclosure of which is incorporated herein by reference in itsentirety. The parent claim priority to Japanese Application No.2004-326086, the disclosure of which is incorporated herein by referencein its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a metal-clad laminate having a film(which film is hereinafter referred to as a thermoplastic liquid crystalpolymer film) including a thermoplastic polymer capable of forming anoptically anisotropic melt phase (which thermoplastic polymer ishereinafter referred to as a thermoplastic liquid crystal polymer), anda method for producing such metal-clad laminate. More specifically, themetal laminate obtained in accordance with the present invention has notonly excellent properties such as low moisture absorbability, heatresistance, chemical resistance and electrical properties deriving fromthe thermoplastic liquid crystal polymer film, but also excellentdimensional stability and is useful as materials for a flexible electricwiring board and for a circuit board on which semiconductor devices ismounted.

2. Description of the Related Art

In recent years, demands for scale reduction and weight reduction ofportable electronic devices such as mobile communication devices havecome to be pressing, and high density mounting has come to beincreasingly expected. In accordance with the demands, use has been madeof multi-layered wiring boards, reduced wiring pitches, fine via holes,and small-size multiple-pin IC packages and, along therewith, the scalereduction and surface mounting of passive elements such as capacitorsand resistors are taking place. In particular, as an effective approach,there have been mentioned techniques of forming those passive elementsdirectly on a surface of and/or inside the printed wiring board or thelike and techniques of directly mounting active elements such as ICpackages on a surface of the printed wiring board, and these techniquesare effective not only to achieve a high density mounting, but toincrease the reliability. As a result, requirements for the dimensionalstability of the wiring boards have come to be highly developed, thatis, the stable rate of change in dimension before and after formation ofsemiconductor circuits as well as before and after the heating processused to mount the active and/or passive elements has been required. Inaddition, the necessity to eliminate the anisotropy of the wiring boardshas come to be increasing.

The thermoplastic liquid crystal polymer film having excellentproperties such as low moisture absorbability, heat resistance, chemicalresistance and electrical properties has been rapidly commercialized asa material for an insulation substrate which improves reliability ofprinted wiring boards.

Hitherto, manufacture of a metal-clad laminate by laminating athermoplastic liquid crystal polymer film and a metallic sheet togetherhas been carried out by the utilization of a vacuum hot press apparatus.This lamination is conducted by a process in which while thethermoplastic liquid crystal polymer film and the metallic sheet areplaced in between two hot plates, the both are thermally compressed tobond them together under a vacuum atmosphere, and this process is calledas a vacuum hot press lamination process. In order to obtain themetal-clad laminate excellent in dimensional stability, with thislamination method, the coefficients of longitudinal and transversethermal expansion of the thermoplastic liquid crystal polymer film usedas a raw material must be adjusted to a value approximating to thethermal expansion coefficient of the metallic sheet and by so doing, theanisotropy in dimensional stability can be eliminated. However, sincethe vacuum hot press lamination process is a sheet-feed typemanufacturing process, a large length of time such as material settingtime, press work time for one cycle, and time required to remove thematerial after the press work is necessary to complete production of onemetal-clad laminate, and the production rate is therefore lowered. If anattempt is made to improve the machine and equipments so that a numberof products can be manufactured all at a time with the production rateincreased, the machine and equipments tend to become bulky in size andcostly, resulting in increase of the cost. Accordingly, development of acontinuous manufacturing method capable of alleviating the foregoingproblems has hitherto been desired for.

On the other hand, in order to provide the full features of thethermoplastic liquid crystal polymer film and, further, to bring out thesuperiority thereof in terms of cost, continuous lamination with themetallic sheet has to be embodied and this has hitherto been deliberatedin various fields. By way of example, conditions necessary to improvethe adhesive force between the polymer film and the metallic sheet and atechnique for improving the mechanical strength (See, for example, theJP Laid-open Patent Publication No. H05-42603.) have been well known inthe art. The method of treating a thermoplastic liquid crystal polymerfilm, particularly a technology concerning the rate of change indimension upon heating of the thermoplastic liquid crystal polymer film(See, for example, the JP Laid-open Patent Publication No. H08-90570.)has also been well known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view showing one example of an apparatus forperforming a method of continuously manufacturing a metal-clad laminateaccording to an embodiment of the present invention.

FIG. 2 is a schematic side view showing one example of an apparatus formanufacturing a thermoplastic liquid crystal polymer film that isemployed in the metal-clad laminate according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

However, the JP Laid-open Patent Publication No. H05-42603 is silent asto the manner of improving the dimensional stability of thethermoplastic liquid crystal polymer film and, similarly, the JPLaid-open Patent Publication No. H08-90570 is also silent as to thecharacteristics of the metal-clad laminate. In addition, with thetechniques disclosed in each of those prior art patent documents, it isdifficult to obtain continuously and in a stabilized fashion, themetal-clad laminate excellent in isotropy and dimensional stability. Inother words, in the case where the thermoplastic liquid crystal polymerfilm and the metallic sheet are thermally compressed to bond themtogether at a nipping region between the heating rolls, molecules of thethermoplastic liquid crystal polymer film are apt to be oriented in thelongitudinal direction by at least the effect of the tension broughtabout by the weight of the film itself in a direction longitudinallythereof (in a pulling direction) in a free run region defined by amaterial feed apparatus and the heating rolls, and by the pressureimposed on the film in a direction longitudinally thereof at the nippingregion between the heating rolls. As a result thereof, it is difficultto provide the metal-clad laminate excellent in isotropy and dimensionalstability.

An object of the present invention is to provide a metal-clad laminate,and a method for production thereof, which is effective to provide ametal-clad laminate excellent in isotropy, appearance, adhesive forcebetween the polymer film and the metallic sheet, and dimensionalstability with high productivity by the use of a continuousmanufacturing technique using the heating rolls.

In order to accomplish the foregoing objects of the present invention,there is provided a method of producing a metal-clad laminate of a kindincluding a thermoplastic liquid crystal polymer film and a metallicsheet bonded to at least one surface of the film, which method includesa first step of thermally compressing the metallic sheet and thethermoplastic liquid crystal polymer film at a nipping region betweenheating rolls to bond them together to provide a metal-clad laminate,wherein a coefficient α_(L) (×10⁻⁶° C.) of thermal expansion in thelongitudinal direction, a thickness T (μm), a thickness coefficientβ(×10⁻⁶/ μm·° C.) and an anisotropy coefficient γ(×10⁻⁶° C.) of thethermoplastic liquid crystal polymer film satisfy the equation, α_(L)=βT+γ, and wherein the thickness coefficient β is within the range of −0.08to −0.01, that is, (−0.08 ≦β≦−0.01), the anisotropy coefficient γrelative to a thermal expansion coefficient (α_(M)) of the metallicsheet is within the range of +6 to +10(×10⁻⁶/° C.), that is, (α_(M)+6≦γ≦α_(M)+10), and a coefficient α_(T) of thermal expansion in thetransverse direction of the polymer film relative to the thermalexpansion coefficient α_(m) of the metallic sheet is within the range of−2 to +3(×10⁻⁶/° C.), that is, (α_(M)−2≦α_(T)≦α_(M) +3); and a secondstep of heat treating the resultant metal-clad laminate at a heattreating temperature equal to or lower than the melting point of thethermoplastic liquid crystal polymer film.

As hereinabove described, when the stretched thermoplastic liquidcrystal polymer film and the metallic sheet are thermally compressed tobond them together as they are passed through the nipping region betweenthe heating rolls, anisotropy in the longitudinal thermal expansion isdeveloped in the thermoplastic liquid crystal polymer film by the effectof the tension acting on those materials in the longitudinal directionof the film, and the pressure imposed on the film in the longitudinaldirection thereof by the heating rolls. According to the presentinvention, by the use of the thermoplastic liquid crystal polymer filmhaving the thermal expansion coefficients α_(L) and α_(T) of the film inthe lengthwise (longitudinal) direction and the widthwise (transverse)direction falling within the specified ranges, respectively, during thefirst step when the thermoplastic liquid crystal polymer film and themetallic sheet are thermally compressed as they pass through the nippingregion between the heating rolls while a tension is applied continuouslyto the film in the longitudinal direction thereof, such anisotropy canbe counterbalanced by the molecular orientation of the thermoplasticliquid crystal polymer film, tending to orient the molecules in adirection transverse to the longitudinal direction of the film, therebyeliminating the anisotropy of the thermal expansion coefficient of thethermoplastic liquid crystal polymer film. As a result, the metal-cladlaminate excellent in isotropy and appearance can be obtained stably.Also, when a heat treatment is performed on the resultant metal-cladlaminate under a specific temperature condition, the strong bondabilitybetween the polymer film and the metallic sheet is achieved to providethe metal-clad laminate excellent in dimensional stability having adesired rate of dimensional change. In this way, the metal-clad laminateexcellent in isotropy, appearance, bondability between the polymer filmand the metallic sheet, and dimensional stability can be obtained with ahigh productivity resulting from the continuous manufacture with the useof the heating rolls.

Although raw materials of the thermoplastic liquid crystal polymer to beused in the present invention is not specifically limited, specificexamples of such thermoplastic liquid crystal polymer may includewell-known thermotropic liquid crystal polyesters and thermotropicliquid crystal polyester amides, which can be prepared from compoundsand the derivatives thereof, classified into the following exemplifiedcompounds (1) to (4). It is, however, to be noted that in order toobtain a polymer capable of forming an optically anisotropic melt phase,various combination of those raw compounds has nevertheless their ownproper mixing ranges.

(1) Aromatic or aliphatic dihydroxy compounds. (As for typical examples,see Table 1 below.)

TABLE 1 Chemical formulae of typical examples of aromatic or aliphaticdihydroxy compounds

HO(CH₂)_(n)OH (n is an integer of 2 to 12)

(2) Aromatic or aliphatic dicarboxylic acids. (As for typical examples,see Table 2 below.)

TABLE 2 Chemical formulae of typical examples of aromatic or aliphaticdicarboxylic acids

HOOC(CH₂)_(n)COOH (n is an integer of 2 to 12)

(3) Aromatic hydroxycarboxylic acids. (As for typical examples, seeTable 3 below.)

TABLE 3 Chemical formulae of typical examples of aromatichydroxycarboxylic acids

(4) Aromatic diamines, aromatic hydroxyamines or aromaticaminocarboxylic acids. (As for typical examples, see Table 4 below.)

TABLE 4 Chemical formulae of typical examples of aromatic diamines,aromatic hydroxyamines or aromatic aminocarboxylic acids

Typical examples of the thermoplastic liquid crystal polymer obtainedfrom these compounds include copolymers (a) to (e) having structuralunits shown in Table 5.

TABLE 5 Typical examples of thermoplastic liquid crystal polymer (a)

(b)

(c)

(d)

(e)

In addition, the thermoplastic liquid crystal polymer to be used in thepresent invention preferably has a melting point within the range offrom about 200 to about 400° C., more preferably within the range offrom about 250 to about 350° C. in order to render the resultant film tohave a desirable heat resistance and a workability. In the case wherethe film requires a higher heat resistance and melting point, the heatresistance and melting point of the film can be increased to a desireddegree if the resultant film once obtained is subjected to a heattreatment. As one example of the heat treatment, with the film onceobtained, which has a melting point of 283° C., the melting point of thefilm can be increased to 320° C. if such film is heated at 260° C. for 5hours.

The thermoplastic liquid crystal polymer film used in the presentinvention can be obtained by extrusion-molding of the above-mentionedthermoplastic liquid crystal polymer. At this time, although anyextrusion molding methods can be employed, industrially advantageous oneincludes T-die film forming and stretching method, laminate stretchingmethod, inflation method and the like. Particularly with the inflationmethod, stresses can be applied not only in a direction of themechanical axis of the film (the longitudinal direction of the filmreferred to above) (which direction is hereinafter referred to as “MDdirection”), but also in a direction perpendicular to the MD direction(the transverse direction of the film referred to above) (whichdirection is hereinafter referred to as “TD direction”) and, therefore;it possible to obtain the film, of which mechanical properties andthermal characteristics in both of the MD direction and the TD directionare well counterbalanced with each other.

The thermoplastic liquid crystal polymer film referred to above isrequired to have a coefficient α_(L) (×10⁻⁶/° C.) of thermal expansionin the longitudinal direction of the film, which coefficient in relationto a thickness T (μm), a thickness coefficient β (×10⁻⁶/μm·° C.) and ananisotropy coefficient γ (×10⁻⁶/° C.) of the film, satisfies theequation, α_(L)=βT+γ. At the same time, the thickness coefficient β, theanisotropy coefficient γ relative to a thermal expansion coefficient(α_(M)) of the metallic sheet and a coefficient α_(T) of thermalexpansion of the film in the transverse direction relative to thethermal expansion coefficient α_(M) of the metallic sheet must be withinthe range of −0.08 to −0.01, i.e., (−0.08≦β≦−0.01), the range of +6 to+10 (×10⁻⁶/° C.), i.e., (α_(M)+6≦γ≦α_(M)+10), and the range of −2 to+3(×10⁻⁶/° C.), i.e., (α_(M)−2≦α_(T)≦α_(M)+3), respectively. Therequired thermal expansion coefficient of the thermoplastic liquidcrystal polymer film may vary, depending on fields of application,within the specific range discussed above. The thermoplastic liquidcrystal polymer film having the thermal expansion coefficient withinthis specific range has a mechanical property and a thermalcharacteristic in both of the MD and TD directions, which are notbalanced with each other. The thermoplastic liquid crystal polymer film,however, does not pose any practical problem and is, as will bediscussed later, advantageous in improvement in isotropy, appearance,bondability between the polymer film and the metallic sheet, anddimensional stability when such film is eventually used to form themetal-clad laminate.

The thermal expansion coefficient of the film referred to above isdefined as the coefficient obtained by dividing the degree of thermalexpansion of such film by a temperature difference, when such film isheated from a room temperature to a temperature approximating to thethermal deformation temperature of the film at a predeterminedtemperature raising rate. This thermal expansion coefficient of the filmcan be calculated by the following manner.

First the known apparatus for thermomechanical analysis is employed, anda strip of film cut from the thermoplastic liquid crystal polymer filmis fixed at one end of the apparatus and allowed to apply a tensile loadat the opposite end thereof Thereafter the amount of thermal expansionof the film strip, which is exhibited when the film strip is heated at aconstant temperature raising rate, is measured. By way of example,assuming that the film strip has a length L0 (mm) as measured in adirection in which the tensile load is applied, and a length L1 (mm) asmeasured in a direction when heated, and that the room temperature andthe heating temperature are expressed by T1 (° C.) and T2 (° C.),respectively, the thermal expansion coefficient can be calculated fromthe following equation:α_(L)=[(L1−L0)/(T2−T1)]/L0(×10⁻⁶° C.)

In the present invention, the parameters L0, T2 and T1 are chosen to be20 mm, 150° C. and 25° C., respectively, and the tensile load is chosento be 1 gr.

The coefficient α_(L) (×10⁻⁶/° C.) of thermal expansion in thelongitudinal (MD) direction of the film used in the practice of thepresent invention satisfies, in relation to the thickness T (μm), thethickness coefficient β (×10⁻⁶μm ·° C.) and the anisotropy coefficient γ(×10⁻⁶ cm/cm/° C) of such film, the equation of α_(L)=βT +γ. Thisequation is designed with the thickness of the film taken intoconsideration with respect to the longitudinal thermal expansioncoefficient α_(L).

The thickness coefficient β referred to above is required to be withinthe range of −0.08 to −0.01, that is, (−0.08≦β≦−0.01). If the thicknesscoefficient β is greater than −0.01 or smaller than −0.08, the resultantmetal-clad laminate will exhibit an unsatisfactory dimensionalstability, and a considerable anisotropy will occur between the MD andTD directions. In particular, in the field of application where a highdimensional stability is required, the thickness coefficient β ispreferred to be within the range of −0.07 to −0.02.

The anisotropy coefficient γ referred to above is required to be,relative to the thermal expansion coefficient α_(M) if the metallicsheet, within the range of +6 to +10 (×10⁻⁶/° C.), that is,(α_(M)+6≦γ≦α_(M)+10). If the anisotropy coefficient γ is smaller than(α_(M) +6) or greater than (α_(M)+10), the resultant metal-clad laminatewill exhibit an unsatisfactory dimensional stability and a considerableanisotropy will occur between the MD and TD directions. By way ofexample, in the case of the metallic sheet being a copper foil, sincethe copper foil has a thermal expansion coefficient of 18 (×10⁻⁶° C.),the anisotropy coefficient γ is within the range of 24 to 28. In thecase of the metallic sheet being an aluminum foil, since the aluminumfoil has a thermal expansion coefficient of 23 (×10⁻⁶° C.), theanisotropy coefficient γ is within the range of 29 to 33.

The coefficient α_(T) of thermal expansion of the film in the widthwise(TD) direction is required to be within the range of −2 to +3 (×10⁻⁶°C.) relative to the thermal expansion coefficient α_(M) of the metallicsheet, that is, α_(M)−2≦α_(T)≦α_(M)+3. By way of example, in the case ofthe metallic sheet being a copper foil, the thermal expansioncoefficient α_(T) is within the range of 16 to 21. In the case of themetallic sheet being an aluminum foil, the thermal expansion coefficientα_(T) is within the range of 21 to 26. The thermal expansion coefficientα_(T) referred to above is preferably within the range ofα_(M)≦α_(T)≦α_(M)+2.

The thickness T of the thermoplastic liquid crystal polymer film of thepresent invention is preferably within the range of 10 to 250 μm, i.e.,10≦T≦250. It is, however, to be noted that where the metal-clad laminateutilizing the thermoplastic liquid crystal polymer film as anelectrically insulating material is used as a flexible printed wiringboard, the film thickness of such film is more preferably within therange of 20 to 100 μm and, particularly preferably, within the range of20 to 50 μm. If the thickness of such film is too small, the rigidityand the strength of the film will decrease to such an extent as toconstitute a cause of deformation of the resultant printed circuit boarddue to the imposed pressure at the time of mounting electronic componentparts on such printed wiring board, which deformation eventually leadsto undesirable reduction of the positional precision of the wiring. Itis to be noted that additives such as, for example, a lubricating agentand/or antioxidant and/or filler materials may be mixed in thecomposition of the film.

In any event, the present invention will become more clearly understoodfrom the following description of preferred embodiments thereof, whentaken in conjunction with the accompanying drawings. However, theembodiments and the drawings are given only for the purpose ofillustration and explanation, and are not to be taken as limiting thescope of the present invention in any way whatsoever, which scope is tobe determined by the appended claims. In the accompanying drawings, likereference numerals are used to denote like parts throughout the severalviews, and:

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 illustrates an example of an apparatus for manufacturing athermoplastic liquid crystal polymer film used for a metal-clad laminateof the present invention and which has respective coefficients α_(L) andα_(T) of thermal expansion in lengthwise (longitudinal) and widthwise(transverse) directions falling within specific ranges. The illustratedapparatus makes a laminated sheet 20 made up of a thermoplastic liquidcrystal polymer film 12, which is drawn outwardly from a supply roll 11,and a support 14 such as, for example, an aluminum foil drawn outwardlyfrom a supply roll 13, the both of which are, while overlapped one abovethe other, thermally compressed to bond them together as they aresupplied to a heating roll assembly 15.

For the heating roll assembly 15, a pair of metallic heating rolls or acombination of a heating roll made of a heat resistant rubber and ametallic heating roll are employed. In the manufacture of the laminatedsheet 20 shown in FIG. 2, the combination of the heat-resistant rubberheating roll 51 and the metallic heating roll 52 are employed, with theheat-resistant rubber heating roll 51 and the metallic heating roll 52positioned on respective sides of the film 12 and the support 14. Bythis arrangement, unnecessary adhesion of the film to the metallicheating roll 52 can be avoided.

Thereafter, the laminated sheet 20 is supplied to a heat treatment unit16, where the laminated sheet 20 is heat treated at a temperature withinthe range of a value lower by 10° C. than the melting point of thethermoplastic liquid crystal polymer film 12 and a value higher by 10°C. than the melting point thereof. When the heat treatment is carried atthe temperature within the range of the value 10° C. lower than themelting point of the thermoplastic liquid crystal polymer film 12 andthe value 10° C. higher than the melting point thereof, the thermalexpansion coefficients of the thermoplastic liquid crystal polymer film12 can be increased. Then the laminated sheet 20 is subsequently peeledoff by two upper and lower peeling rolls 17 and 17, and a thermoplasticliquid crystal polymer film 2 having desired thermal expansioncoefficients is provided by separating the thermoplastic liquid crystalpolymer film 2 from the support 14. In this way, the thermoplasticliquid crystal polymer film 2 can be obtained, which has thecoefficients α_(L) and α_(T) of thermal expansion in the lengthwise andwidthwise directions, respectively, falling within the specific rangesdiscussed above. For the heat treatment apparatus 16, any known meanssuch as a hot blast circulating furnace, a hot roll or a ceramic heatercan be employed.

FIG. 1 illustrates an example of an apparatus for performing the methodof continuously manufacturing the metal-clad laminate of the presentinvention. This apparatus makes a one-side metal-clad laminate 10 madeup of the thermoplastic liquid crystal polymer film 2, which has madeusing the apparatus shown in FIG. 2, and has the coefficients α_(L) andα_(T) of thermal expansion in the lengthwise and widthwise directions,respectively, falling within the specific ranges discussed above, and ametallic sheet 4 such as a copper foil. During a first process step ofthe apparatus, the thermoplastic liquid crystal polymer film 2 and themetallic sheet 4 are drawn outwardly from a supply roll 1 and a supplyroll 3, respectively, and the both of them are, while overlapped oneabove the other, thermally compressed to bond them together as they aresupplied to a heating roll assembly 5. For this heating roll assembly 5,a pair of metallic heating rolls or a combination of a heating roll madeof a heat resistant rubber and a metallic heating roll are employed. Inthe case of the manufacture of this one-sided metal-clad laminate 10referred to above, the combination of the heat-resistant rubber heatingroll 51 and the metallic heating roll 52 are employed in a mannersimilar to that described hereinabove.

When during the first process step, the layered product of the polymerfilm 2 and the metallic sheet 4 are, while a tension is applied theretoin a direction lengthwise of the film, supplied through the heating rollassembly 5 in a fashion, in which the thermoplastic liquid crystalpolymer film 2 and the metal sheet 4 are overlapped one above the other,and then thermally compressed to bond them together by a pressure whichis applied in a lengthwise direction of the film at a nipping regionbetween heating rolls 51 and 52, the both can be laminated to give ametal-clad laminate 10. At this time, as a result of using thethermoplastic liquid crystal polymer film 2 having the coefficientsα_(L) and α_(T) of thermal expansion in the lengthwise and widthwisedirections, respectively, falling within the specific ranges discussedabove, the anisotropy of thermal expansion in the lengthwise directionof the film, which occurs in the thermoplastic liquid crystal polymerfilm 2, can be counterbalanced with the orientation of molecules of thepolymer film 2 in which the molecules are oriented in a directiontransverse to the lengthwise direction of the film, when the thermalcompression is effected at the nipping region between the heating rolls51 and 52 while the tension has been applied continuously in thelengthwise direction of the film. In this way, since the anisotropy ofthe thermal expansion coefficient of the thermoplastic liquid crystalpolymer film 2 is removed, the metal-clad laminate 10 excellent inisotropy and appearance can be obtained in a stable manner.

This apparatus then operates to supply the metal-clad laminate 10obtained during the first process step to a heat treating unit 6, andduring a second process step, the metal-clad laminate 10 is heat treatedat a heating temperature not higher than the melting point of thethermoplastic liquid crystal polymer film 2. By so doing, the metal-cladlaminate 10can be obtained, which exhibits a high force of bondingbetween the polymer film 2 and the metallic sheet 4 and an excellentdimensional stability having a desired rate of change in dimension. Inorder to increase the force of bonding between the polymer film 2 andthe metallic sheet 4, the heating temperature is preferably within therange of a value lower by 5° C. than the melting point of the film 2 anda value lower by 20° C. than the melting point thereof. If the heatingtemperature exceeds the melting point, foaming and/or considerablechange in thermal expansion coefficient will occur and the quality ofthe film may not be developed to a desired extent. On the other hand, ifthe heating temperature is lower by 20° C. than the melting point, itwill not contribute to increase of the force of bonding between thepolymer film 2 and the metallic sheet 4 and it may occur that, dependingon the type of the metallic sheet 4 to be used, no required bondingforce will be satisfied. For the heat treating unit 6, a hot blastcirculating furnace, a hot roll or a ceramic heater can be employed in amanner similar to that hereinbefore described. After this second processstep, the metal-clad laminate 10 is wound up by and around a windingroll 7 in a roll form.

Hereinafter, the present invention will be described in detail by way ofExamples, but the present invention is in no way limited by thoseExamples. It is to be noted that in the following Examples, the meltingpoint of the thermoplastic liquid crystal polymer film, and bondingstrength and dimensional stability of the metal-clad laminate wereevaluated in the following manners.

(1) Melting Point

Using a differential scanning calorimeter, the thermal behavior of thefilm was observed to determine the melting point. In other words, afterthe temperature of the test film was raised at a rate of 20° C./min tocompletely melt the film, the molten product was rapidly cooled down to50° C. at a rate of 50° C./min and, then, the position of the heatabsorption peek appearing when the temperature thereof was again raisedat a rate of 20° C./min was recorded as the melting point of the film.

(2) Bonding Strength

A test piece having a width of 1.5 cm was prepared from the laminate,and the film layer of the test piece was then fixed to a flat plate by adouble-sided bonding tape, and the bonding strength (kg/cm), at whichthe metallic foil of the test piece separates from the film layer, wasmeasured by peeling the metallic foil from the film layer at a rate of50 mm/min by the 180° method in accordance with JIS C 5016.

(3) Dimensional Stability of Laminate

The dimensional stability was measured according to IPC-TM-6502.2.4.

REFERENCE EXAMPLE 1

A thermoplastic liquid crystal polymer, which was a copolymer ofp-hydroxy benzoic acid and 6-hydroxy-2-naphthoic acid and had a meltingpoint of 280° C. was melt-extruded and was then formed into films,having respective film thicknesses of 25, 50, 100 and 225 μm, by aninflation molding method under a condition in which the ratio of drawingin longitudinal and transverse directions was controlled. Each of thoseresultant films, after having been overlapped with a respective aluminumfoil which had a film thickness of 30 μm and was applied thereon with amold releasing agent, was thermally compressed to bond to the metallicfoil by passing them through a nipping region between a metallic heatingroll of 260° C. and a heat resistant rubber roll under a pressure of 20kg/cm², and was subsequently heat treated for 30 seconds in a heatingfurnace, which had been heated to a temperature required for thecoefficient of thermal expansion α_(L) of each of those films having thedifferent film thickness in the MD direction to attain the followingrespective value. Thereafter, each of those laminated films was heattreated for six hours in an oven at 260° C. under the nitrogenatmosphere, followed by peeling off the aluminum foil from therespective film to provide a respective thermoplastic liquid crystalpolymer film having a melting point of 305° C., a thermal expansioncoefficient α_(T) of 19×10⁻⁶ cm/cm/° C. in the TD direction and athermal expansion coefficient α_(L) of 25.3, 24.5, 23 or 19.3 (×10⁻⁶/°C.) (β=−0.03 and γ=26) in the MD direction. Those thermoplastic liquidcrystal polymer films are hereinafter referred to as the thermoplasticliquid crystal polymer film A.

In Reference Example 1 described above, for example, in the case wherethe thermoplastic liquid crystal polymer film A and the copper foil(metallic sheet) are laminated together, the requirement of (10≦T≦250)is satisfied because the thickness of the film is one of 25, 50, 100 and225 μm; the requirement of (−0.08≦β≦−0.01) is satisfied because thethickness coefficient β is −0.03; and the requirement of(α_(M)+6≦γ≦α_(M) +10) is satisfied because the anisotropy coefficientγis 26 and the thermal expansion coefficient α_(M) of the copper foil is18 (×10⁻⁶/° C.). Because the thermal expansion coefficient α_(T) is 19(×10⁻⁶/° C.) for all the films, the requirement of (α_(M)−2≦α_(T)≦α_(M)+3) is satisfied. The thermal expansion coefficient α_(L)matches with the calculated result of (βT+γ) when the thickness T, thethickness coefficient β and the anisotropy coefficient γ aresubstituted, i.e., (α_(L)=βT +γ). Thus, the thermoplastic liquid crystalpolymer film A has those parameters falling within the respective rangesthat are required in the practice of the present invention.

REFERENCE EXAMPLE 2

A thermoplastic liquid crystal polymer, which was a copolymer ofp-hydroxy benzoic acid and 6-hydroxy-2-naphthoic acid and had a meltingpoint of 280° C. was melt-extruded and was then formed into films,having respective film thicknesses of 25, 50, 100 and 225 μm, by aninflation molding method under a condition, in which the ratio ofdrawing in longitudinal and transverse directions was controlled. Eachof those resultant films, after having been overlapped with a respectivealuminum foil which had a film thickness of 30 μm and was appliedthereon with a mold releasing agent, was thermally compressed to bond tothe aluminum foil by passing them through a nipping region between ametallic heating roll of 260° C. and a heat resistant rubber roll undera pressure of 20 kg/cm², and was subsequently heat treated for 30seconds in a heating furnace, which had been heated to a temperaturerequired for the coefficient of thermal expansion α_(L) of each of thosefilms of the different film thickness in the MD direction to attain thefollowing respective value. Thereafter, each of those laminated filmswas heat treated for six hours in an oven at 260° C. under the nitrogenatmosphere, followed by peeling off the aluminum foil from therespective film to provide a respective thermoplastic liquid crystalpolymer film having a melting point of 305° C., a thermal expansioncoefficient α_(T) of 19 (×10⁻⁶/° C.) in the TD direction and a thermalexpansion coefficient α_(L) of 23.5, 23, 22 and 19.5 (×10⁻⁶/° C.)(β=−0.02 and γ=24) in the MD direction. Those thermoplastic liquidcrystal polymer films are hereinafter referred to as the thermoplasticliquid crystal polymer film B.

In Reference Example 2 described above, where the thermoplastic liquidcrystal polymer film B and the copper foil (metallic sheet) arelaminated together in a manner similar to that in Reference Example 1above, the requirement of the thickness T is similarly satisfied; therequirement of (−0.08≦β≦−0.01) is satisfied because the thicknesscoefficient β is −0.02; and the requirement of (α_(M)+6≦γ≦α_(M)+10) issatisfied because the anisotropy coefficient γ is 24 and the thermalexpansion coefficient α_(M) of the copper foil is 18 (×10⁻⁶° C.).Because the thermal expansion coefficient α_(T) is 19 (×10⁻⁶° C.) forall the films, the requirement of (α_(M)−2≦α_(T)≦α_(M)+3) is satisfied.The thermal expansion coefficient α_(L) matches with the calculatedresult of (βT+γ) when the thickness T, the thickness coefficient β andthe anisotropy coefficient γ are substituted, i.e., (α_(L)=βT +γ). Thus,the thermoplastic liquid crystal polymer film B has those parametersfalling within the respective ranges that are required in the practiceof the present invention.

REFERENCE EXAMPLE 3

A thermoplastic liquid crystal polymer, which was a copolymer ofp-hydroxy benzoic acid and 6-hydroxy-2-naphthoic acid and had a meltingpoint of 280° C. was melt-extruded and was then formed into films,having respective film thicknesses of 25, 50, 100 and 225 μm, by aninflation molding method under a condition, in which the ratio ofdrawing in longitudinal and transverse directions was controlled. Eachof those resultant films, after having been overlapped with a respectivealuminum foil which had a film thickness of 30 μm and was appliedthereon with a mold releasing agent, was thermally compressed to bond tothe aluminum foil by passing them through a nipping region between ametallic heating roll of 260° C. and a heat resistant rubber roll undera pressure of 20 kg/cm², and was subsequently heat treated for 30seconds in a heating furnace, which had been heated to a temperaturerequired for the coefficient of thermal expansion α_(L) of each of thosefilms of the different film thickness in the MD direction to attain thefollowing respective value. Thereafter, each of those laminated filmswas heat treated for six hours in an oven at 260° C. under the nitrogenatmosphere, followed by peeling off the aluminum foil from therespective film to provide a respective thermoplastic liquid crystalpolymer film having a melting point of 305° C. and thermal expansioncoefficients α_(T) and α_(L) of 18 (×10⁻⁶° C.)(β=0 and γ=18) in both ofthe TD and MD directions. Those thermoplastic liquid crystal polymerfilms are hereinafter referred to as the thermoplastic liquid crystalpolymer film C.

In Reference Example 3 described above, where the thermoplastic liquidcrystal polymer film C and the copper foil (metallic sheet) arelaminated together in a manner similar to that in Reference Example 1,the requirement of the thickness T is similarly satisfied; therequirement of (−0.08≦β≦−0.01) is not satisfied because the thicknesscoefficient β is 0; and the requirement of (α_(M)+6≦γ≦α_(M)+10) is notsatisfied either because the anisotropy coefficient γ is 18 and thethermal expansion coefficient α_(M) of the copper foil is 18(×10⁻⁶° C.).Because the thermal expansion coefficient α_(T) is 18 (×10⁻⁶/° C.) forall the films, the requirement of (α_(M)−2 ≦α_(T)≦α_(M)+3) is satisfied.The thermal expansion coefficient α_(L)matches with the calculatedresult of (βT +γ) when the thickness T, the thickness coefficient β andthe anisotropy coefficient γ are substituted, i.e., (α_(L)=βT+γ). Thus,the thermoplastic liquid crystal polymer film C has the thicknesscoefficient β and the anisotropy coefficient γ , neither of which do notfall within the respective ranges that are required in the practice ofthe present invention.

REFERENCE EXAMPLE 4

A thermoplastic liquid crystal polymer, which is a copolymer ofp-hydroxy benzoic acid and 6-hydroxy-2-naphthoic acid and has a meltingpoint of 280° C. was melt-extruded and was then formed into films,having respective film thicknesses of 25, 50, 100 and 225 μm, by aninflation molding method under a condition, in which the ratio ofdrawing in longitudinal and transverse directions was controlled. Eachof those resultant films, after having been overlapped with a respectivealuminum foil which had a film thickness of 30 μm and was appliedthereon with a mold releasing agent, was thermally compressed to bond tothe aluminum foil by passing them through a nipping region between ametallic heating roll of 260° C. and a heat resistant rubber roll undera pressure of 20 kg/cm², and was subsequently heat treated for 30seconds in a heating furnace, which had been heated to a temperaturerequired for the coefficient of thermal expansion α_(L) of each of thosefilms of the different film thickness in the MD direction to attain thefollowing respective value. Thereafter, each of those laminated filmswas heat treated for six hours in an oven at 260° C. under the nitrogenatmosphere, followed by peeling off the aluminum foil from therespective film to provide a respective thermoplastic liquid crystalpolymer film having a melting point of 305° C., a thermal expansioncoefficients α_(T) of 19 (×10⁻⁶/° C.) in the TD direction and a thermalexpansion coefficient α_(L) of 16.5, 15, 12, 4.5 (×10⁻⁶° C.) (β=−0.06and γ=18) in the MD direction. Those thermoplastic liquid crystalpolymer films are hereinafter referred to as the thermoplastic liquidcrystal polymer film D.

In Reference Example 4 described above, where the thermoplastic liquidcrystal polymer film D and the copper foil (metallic sheet) arelaminated together in a manner similar to that in Reference Example 1,the requirement of the thickness T is similarly satisfied; therequirement of (−0.08≦β≦−0.01) is satisfied because the thicknesscoefficient β is −0.06; and the requirement of (α_(M)+6≦γ≦α_(M)+10) isnot satisfied because the anisotropy coefficient γ is 18 and the thermalexpansion coefficient α_(M) of the copper foil is 18 (×10⁻⁶/° C.).Because the thermal expansion coefficient α_(T) is 19 (×10⁻⁶/C° ) forall of the films, the requirement of (α_(M)−2≦α_(T)≦α_(M)+3) issatisfied. The thermal expansion coefficient α_(L) matches with thecalculated result of (βT+γ) when the thickness T, the thicknesscoefficient β and the anisotropy coefficient γ are similarlysubstituted, i.e., (α_(L)=βT +γ). Thus, the thermoplastic liquid crystalpolymer film D has the anisotropy coefficient γ which do not fall withinthe ranges that is required in the practice of the present invention.

EXAMPLE 1

The thermoplastic liquid crystal polymer film A obtained in theReference Example 1 and an electrolytic copper foil having a thicknessof 18 μm and a thermal expansion coefficient of 18 (×10⁻⁶ cm/cm/° C.)were used. In a continuous hot roll press apparatus, were installed aheating roll made of a heat resistant rubber (90 degree in hardness) anda metallic heating roll. While the tension in the free run region,through which the thermoplastic liquid crystal polymer film A and thecopper foil were introduced to a nipping region between the heatingrolls, was adjusted to 2 kg for a 400 mm width, the thermoplastic liquidcrystal polymer film A and the copper foil were fed to the nippingregion of the heating rolls to allow them to be thermally compressed at300° C. under a pressure of 20 kg/cm² to thereby provide a laminate ofthe thermoplastic liquid crystal polymer film and the electrolyticcopper foil. Thereafter, the laminate so obtained was heat treated for30 seconds under the nitrogen atmosphere in an oven heated to 270° C.Results of tests conducted on the resultant laminate to determine thebonding strength and the dimensional stability are tabulated in Table 6below. As shown in Table 6, the metal-clad laminate excellent in bondingstrength and dimensional stability was obtained.

EXAMPLE 2

In place of the film A, using the thermoplastic liquid crystal polymerfilm B obtained in Reference Example 2, a similar laminate was preparedand was tested as to the bonding strength and the dimensional stability.Results of the test are tabulated in Table 6 below. As shown in Table 6,the metal-clad laminate excellent in bonding strength and dimensionalstability was obtained.

COMPARATIVE EXAMPLE 1

A metal-clad laminate similar to Example 1, but in which thethermoplastic liquid crystal polymer film C obtained in ReferenceExample 3 was employed instead of the thermoplastic liquid crystalpolymer film A, was prepared and tested as to the bonding strength andthe dimensional stability. Results of the tests are tabulated in Table 6below. As shown in Table 6, the dimensional stability of this metal-cladlaminate in the MD direction is unsatisfactory.

COMPARATIVE EXAMPLE 2

A metal-clad laminate similar to Example 1, but in which thethermoplastic liquid crystal polymer film D obtained in ReferenceExample 4 was employed instead of the thermoplastic liquid crystalpolymer film A, was prepared and tested as to the bonding strength andthe dimensional stability. Results of the tests are tabulated in Table 6below. As shown in Table 6, the dimensional stability of this metal-cladlaminate in the MD direction is unsatisfactory.

COMPARATIVE EXAMPLE 3

The thermoplastic liquid crystal polymer film A obtained in theReference Example 1 and an electrolytic copper foil having a thicknessof 18 μm and a thermal expansion coefficient of 18(×10⁻⁶/° C.) wereused. In a continuous hot roll press apparatus, were installed a heatingroll made of a heat resistant rubber (90 degree in hardness) and ametallic heating roll. While the tension in the free run region, throughwhich the thermoplastic liquid crystal polymer film A and the copperfoil were introduced to a nipping region between the heating rolls, wasadjusted to 2 kg for a 400 mm width, the thermoplastic liquid crystalpolymer film A and the copper foil were fed to the nipping region of theheating rolls to allow them to be thermally compressed at 300° C. undera pressure of 20 kg/cm² to thereby provide a laminate of thethermoplastic liquid crystal polymer film and the electrolytic copperfoil. Results of tests conducted on the resultant laminate to determinethe bonding strength and the dimensional stability are tabulated inTable 6 below. As shown in Table 6, the metal-clad laminate hasexhibited an unsatisfactory bonding strength because the processemployed to prepare the laminate for this Comparative Example did notinclude the second process step employed in the practice of the presentinvention.

TABLE 6 Dimensional Thickness Anisotropy Bonding Stability (%)Coefficient Coefficient Strength MD TD β Y (kg/cm) Direction DirectionEx. 1 −0.03 26 1.2 −0.01 +0.01 Ex. 2 −0.02 24 1.3 +0.01 +0.01 Com. 0 181.0 +0.25 +0.01 Ex. 1 Com. −0.06 18 1.2 +0.20 +0.01 Ex. 2 Com. −0.03 260.7 −0.01 +0.01 Ex. 3

The invention claimed is:
 1. A metal-clad laminate comprising: athermoplastic liquid crystal polymer film consisting of a thermoplasticliquid crystal polymer capable of forming an optically anisotropic meltphase; and a metallic sheet bonded to at least one surface of the film,wherein a melting point of the thermoplastic liquid crystal polymer isfrom 283 to 400° C.; the thermoplastic liquid crystal polymer film is anextruded and molecular-oriented film with molecular orientation in adirection transverse to a lengthwise direction of the film; acoefficient of thermal expansion of the thermoplastic liquid crystalpolymer film in the transverse direction (αT) in the laminate afterthermal compression and heat treatment with the metallic sheet isrelated to a thermal expansion coefficient (αM) of the metallic sheetaccording to:(αM−2)(10⁻⁶/° C.)≦αT≦(αM+3) (10⁻⁶/° C.); a coefficient of thermalexpansion of the thermoplastic liquid crystal polymer film in thelengthwise direction (αL) in the laminate after thermal compression andheat treatment with the metallic sheet is related to the thermalexpansion coefficient (αM) of the metallic sheet according to:(αM−2)(10⁻⁶/° C.)≦αT≦(αM+3) (10⁻⁶/° C.).
 2. The metal-clad laminateaccording to claim 1, wherein the coefficients of thermal expansion inthe transverse direction (αT) and the lengthwise direction (αL) are(αM−2)(10⁻⁶/° C.)≦αT≦(αM+3) (10⁻⁶/° C.), and(αM−2)(10⁻⁶/° C.)≦αT≦(αM+3) (10⁻⁶/° C.), respectively.
 3. The metal-cladlaminate according to claim 1, wherein a metallic sheet is bonded toboth surfaces of the thermoplastic liquid crystal polymer film.
 4. Themetal-clad laminate according to claim 1, wherein the melting point ofthe thermoplastic liquid crystal polymer is from 305 to 400° C.
 5. Themetal-clad laminate according to claim 1, wherein a dimensionalstability of the laminate is within the range of ±0.01% in the MD and TDdirections.